1. Technical Field
The present invention relates to a printing apparatus provided with a transport unit that transports a medium such as a sheet, an imaging unit that images the medium transported by the transport unit, and a print head that prints on the medium, and a printing method.
2. Related Art
In the related art, a printing apparatus provided with a transport unit that transports a medium, such as a sheet, and a print head that prints on the medium transported by the transport unit is widely known as an example of this type of printing apparatus (for example, such as JP-A-2010-284883).
For example, JP-A-2010-284883 discloses a printing apparatus provided with a line-type print head (line head) that discharges ink, a transport unit provided with a rotating roller that transports a medium such as a sheet, a first acquisition unit that acquires rotation information of the rotating roller, and a second acquisition unit that acquires movement information of the medium with a signal processing detecting the surface of the medium during transport. In the printing apparatus, the rotation information of the rotating roller acquired by the first acquisition unit and the movement information of the medium acquired by the second acquisition unit are correlated and stored in memory as correction data for at least one rotation of the rotating roller. The control unit reads out the correction data corresponding to the rotation information of the rotating roller acquired by the first acquisition unit from the memory and performs printing on the medium with the recording timing of the line-type print head corrected. Therefore, even if the transport speed of the medium fluctuates caused by eccentricity of the rotating roller, shifting of the landing position of ink droplets on the medium is suppressed to be low.
In the printing apparatus disclosed in JP-A-2010-284883, the control unit acquires an image of the medium from the imaging unit that forms the second acquisition unit per unit time at a fixed frame rate and acquires rotation information acquired from the detection signal of the encoder that forms the first acquisition unit at a fixed time interval. In this case, even if the time interval at which the rotation information is acquired is the same as the time interval at which the image is acquired, when the time at which the medium is imaged and the time at which the rotation information is acquired are shifted, correction data that includes the shift in the correspondence relationship between the rotation information and the movement information is created. Therefore, even if the discharge timing is corrected based on the movement information acquired from the rotation information with reference to the correction data, the landing position of the ink droplets on the medium shifts in the transport direction of the medium, and this causes the print quality to be lowered.
The same problem arises in a serial printer as in a case of a configuration that performs correction on the transport control based on the rotation information and the movement information. For example, when the transport amount of the medium is corrected based on the shift amount of the correspondence relationship between the rotation information and the movement information during transport of the medium, the correction instead promotes a shift in the next printing position, and promotes a lowering of the print quality due to the shift in printing position. Similarly, in a case of performing error detection based on the rotation information and the movement information, the shift in the correspondence relationship between the rotation information and the movement information becomes a cause of erroneous notification of errors. In this way, in the case of a configuration that performs correction on the control of the printing apparatus based on the rotation information and the movement information, there is concern of the shift of the rotation information and the movement information caused by the shift in the acquisition time of the rotation information and the imaging time of the medium instead leading to defects in the control of the printing apparatus. This type of problem is not limited to a printing apparatus, such as a line printer or a serial printer, and substantially similar problems are present in printing apparatuses in which control is performed based on the rotation information detected by the detecting unit and the movement information based on the image of the medium acquired by the imaging unit.